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Contact Lenses > Tear film assessment and dry eye > Flashcards

Tear film assessment and dry eye Flashcards

1
Q

What is the 2 layer model of the tear film?

A

Made up of a lipid layer and mucoaqueous layer (mucins, proteins and peptides within)

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2
Q

What is the definition of dry eye?

A

A multifactorial disease of the ocular surface caused by a loss of tear film homeostasis, where the tear film is unstable and hyperosmolar, the ocular surface is inflamed and damaged and ocular symptoms occur. Neurosensory abnormalities can play a role in the cause.

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3
Q

What are the types of dry eye?

A

ADDE (Aqueous deficient dry eye)
EDE (Evaporative dry eye)

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4
Q

What causes ADDE?

A

A lack of aqueous production or a low flow rate causes hyperosmolarity - this starts a pathway which causes damage and apoptosis to goblet cells and glycocalyx, causing tear film instability and further hyperosmolarity

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5
Q

What causes EDE?

A

A high evaporation rate of aqueous tears causes hyperosmolarity - this starts a pathway which causes damage and apoptosis to goblet cells and glycocalyx, causing tear film instability and further hyperosmolarity

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6
Q

What are the definite risk factors for dry eye?

A

CL wear
MGD
Age
Sex
Race
Connective tissue disease
Sjogren’s syndrome
VDU use
Androgen deficiency
HRT
Stem cell transplant
Environment
Medications (eg antihistamines, antidepressants)

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7
Q

What are some probable risk factors for dry eye?

A

Diabetes
Rosacea
Viral infection
Thyroid disease
Refractive surgery
Low fatty acid intake

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8
Q

What are some inconclusive risk factors for dry eye?

A

Menopause
Acne
Smoking
Alcohol
Pregnancy
Oral contraceptives
Demodex infestation
Sarcoidosis

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9
Q

What happens to the tear film after CL wear?

A

Lipid layer is thinner and less stable
Osmolarity is increased
Inflammatory mediators are increased (but inflammation is sub-clinical)
The composition of proteins and ions can be altered
The ocular surface temperature decreases

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10
Q

Why does the tear film need to be assessed?

A

Check tear film quantity and quality
Diagnose CLIDE/DE and manage

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11
Q

What makes it difficult to assess the tear film?

A

Thin
Transparent
Moving
Small volume
Easily disturbed - bright light causes tearing and blink pattern changes

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12
Q

What does the ideal test for tear film assessment look like?

A

Quick
Simple
Cheap
Accurate
Repeatable
Minimal invasion
Allows differential diagnosis

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13
Q

What categories of tear film assessment are there?

A

Invasive
Non-invasive
Direct
Indirect
Quality
Quantity

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14
Q

Name some examples of non invasive tear film assessment

A

Questionnaires
Tear meniscus height
Assessing quality
Observing lipid layer
NIBUT
Keratometer

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15
Q

What is a normal tear meniscus height?

A

0.2-0.3mm

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16
Q

What tear meniscus height is considered dry eye?

A

<0.18mm

17
Q

What should you record when assessing tear film quality?

A

Debris
Make up
Mucus threads
Speed of movement

18
Q

How do you measure NIBUT?

A

Project grid onto cornea
Measure time from blink to tear break up 3 times
Record median

19
Q

What is normal for BUT?

A

20-40 secs

20
Q

What BUT is considered dry eye?

A

<10 secs

21
Q

What are lid-parallel conjunctival folds?

A

Folds in bulbar conjunctiva parallel to lid margin caused by friction

22
Q

Name some examples of invasive tear film assessment

A

Tear osmolarity measurement
Schirmer test
Phenol red thread test
FBUT
Ocular surface staining
Lid wiper epitheliopathy

23
Q

How is the Schirmer test carried out?

A

Schirmer strips inserted into lower fornix
Px closes eyes for 5 mins
Amount of tears measured

24
Q

What is a normal result for the Schirmer test?

A

> 10mm

25
Q

What is considered dry eye on Schirmer test?

A

5-9mm borderline
<5mm dry eye

26
Q

How does Phenol red thread test work?

A

Cotton inserted into lower fornix
Alkaline tears change colour of thread
Wetting measured after 15 secs

27
Q

What is a normal result for Phenol red thread test?

A

11-18mm

28
Q

What is considered dry eye on Phenol red thread test?

A

<10mm

29
Q

What are some disadvantages of FBUT?

A

Instillation of NaCl disturbs tear film
NaCl alters the interaction between the layers and reduces surface tension

30
Q

What is considered dry eye on FBUT?

A

<10 secs

31
Q

What is Lid wiper epitheliopathy?

A

Assessment of the lid wiper epithelium using NaCl and Lissamine Green staining

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